Field
The present invention relates to a fuel cell system and a control method therefor.
Related Art
Regarding a fuel gas supply system for supplying a fuel gas (hydrogen) to an anode of a fuel cell (fuel cell stack), there has conventionally been developed a fuel cell system in which fuel gas that has not been consumed by the anode of the fuel cell is circulated to the fuel gas supply system via a circulation pump of a fuel gas circulation system. As an example of this fuel cell system having a fuel gas circulation system, it is disclosed in JP2007-115460A that liquid water condensed on a pipe inner wall of a fuel gas circulation system is discharged by increasing the rotation speed of the circulation pump so as to reduce the possibility that excess liquid water may flow into the circulation pump. Also, it is disclosed in JP2008-171770A that the sounds accompanying the drive of a circulation pump (hydrogen pump) are masked with the sounds accompanying the drive of a compressor or a motor that serves as a load for a fuel cell.
However, in cases where a low-load operation of the fuel cell system is continued for a long time such as where a low-load power generation is continued for a long time, a low-rotation operation of the circulation pump, when continued for a long time, may cause liquid water to reside inside the fuel cell or at particular sites in a fuel gas circulation system, particularly from an outlet of a gas-liquid separator to a suction port of the circulation pump. For example, there are cases where liquid water resides as a result of condensation due to temperature differences between the fuel cell and the circulation pump or liquid water sucked from within the gas-liquid separator by the circulation pump. With this residing water over a specified quantity, there may occur biting of the residing water in the circulation pump during high rotation of the circulation pump. This may lead to generation of abnormal noise or high volume of sounds accompanying the drive of the circulation pump (hereinafter, also referred to as ‘abnormal noise or the like’), thereby problematically giving the user a sense of discomfort or a sense of incompatibility, anxiety for faults and the like.
In addition, when the volume of the residing water in the fuel cell's anode increases, there are problems like a state of insufficient fuel gas supply occurring during high-load power generation, thus leading to a reduction in the voltage of the fuel cell and to a degradation of the electrodes due to oxidation (carbon oxidation).
There are also cases where water discharge is performed not only for the fuel cell's anode-side fuel gas flow path through an increase in the rotational speed of the circulation pump in the fuel gas circulation system, but also for the fuel cell's cathode-side oxidizing gas flow path via the oxidizing gas discharge system through an increase in the rotational speed of the air compressor in the oxidizing gas supply system that supplies the oxidizing gas (airborne oxygen) to the fuel cell's cathode. In this case, there may problematically cause the user to have a sense of discomfort or a sense of incompatibility, anxiety for faults and the like, due to the operation sound that is generated during the anode-side water discharge and the operation sound that is generated during the cathode-side water discharge, especially due to how these operation sounds occur.